1. Field of the invention
The present invention relates to a support device for a probe for the detection and location of possible faults within a bore.
2. Discussion of the Background
Incidents which have occurred in flight by both aircraft and helicopters have revealed that cracks appear in a particularly inaccessible area of the rotor shaft and more specifically at the intersection of two small diameter, internal lubricating ducts. These cracks, initiated during the operation of the aircraft can give rise to the shaft fracturing, engine loss and even to the crashing of the aircraft. It is therefore important during equipment inspection and maintenance operations to check whether such cracks are being formed.
Several inspection methods have been envisaged, including magnetoscopy. This method consists of spraying the part to be inspected with a liquid containing metal particles and subjecting the same to a magnetic field. If there is a crack in the part, an easily measurable stray field then appears. However, this method only makes it possible to detect faults and defects when they have assumed considerable dimensions, i.e. much too late in order to comply with safety requirements.
The aim has therefore been to develop a device for the inspection of parts permitting a particularly early and reliable detection of possible faults. This device is applicable in general terms to the early detection of cracks appearing within a small size bore and which are therefore difficult of access, no matter whether the bore occurs on a rotor shaft or any other mechanical part.
The proposed solution makes use of a probe, more particularly an eddy current inspection probe. This probe constitutes a portable equipment and which is therefore very practical, because it can be used directly at the part inspection location. Moreover, this inspection procedure is reliable. However, it would be desirable to be able to carry out reproducible inspections or checks on the same part and on all the parts of the same batch or series. To this end, it would be desirable to have a support device for the probe permitting the displacement of the latter with respect to the part to be inspected in accordance with predetermined, precise positions.
The prior art already discloses several devices using an eddy current probe for checking a certain number of mechanical parts. Thus, FR-A-2 543 686 describes a support device for an eddy current probe making it possible to place the latter in several predetermined positions with respect to a surface to be analyzed. This support device is specifically designed for the analysis of the external surface of a part and in particular a portion of a rotor, but cannot be used for positioning an eddy current probe within a bore.
FR-A-2 492 527 describes a positioning block for an eddy current inspection probe, said block being positionable on the blade of a turbomachine. For the same reasons as those given hereinbefore, it cannot be used for the inspection of small diameter bores.
U.S. Pat. No. 4,142,154 also discloses a probe for an eddy current inspection probe making it possible to carry out measurements within a bore. The probe used is covered with a protective sleeve. The support is provided with a screw thread actuated by a motor permitting the displacement of said probe in translation within the bore to be inspected. This support also comprises a gear and a motor permitting the rotation of the probe on itself within the bore. However, this device has a complex construction and requires the use of two motors and is therefore complicated to manufacture.
Finally, EP-A-95 845 discloses an inspection apparatus using an eddy current probe for carrying out measurements within a bore. This apparatus has a variable diameter sleeve within which the probe is installed. The apparatus can be manually lowered within the bore to be inspected and a motor rotates the probe on itself.
It should be noted that most of the existing probe-holding devices make use of a motor for the displacements of the probe and consequently have a complex structure.